The disclosure relates generally to porous honeycomb ceramics and more particularly to improved compositions that can be applied to porous honeycomb ceramics.
Ceramic wall flow filters are finding widening use for the removal of particulate pollutants from diesel or other combustion engine exhaust streams. A number of different approaches for manufacturing such filters from channeled honeycomb structures formed of porous ceramics are known. The most widespread approach is to position cured plugs of sealing material at the ends of alternate channels of such structures, which can block direct fluid flow through the channels and force the fluid stream through the porous channel walls of the honeycombs before exiting the filter.
Important aspects of plugging honeycomb structures include plug depth and plug quality. Plug quality is often correlated to the presence of voids in the plugs. In general, the presence of voids can be reduced by reducing the amount of water in the plugging composition and/or increasing the particle size of certain batch components in the plugging composition. However, such modifications can lead to plugs with insufficient depth and, hence, insufficient mechanical (or “push out”) strength.
On the other hand, shorter plugs provide less back pressure, higher filter volume for the same external geometry, thus reducing the frequency of regenerations and improving fuel economy. Moreover, shorter plugs provide better material utilization, thereby reducing filter manufacturing costs. Accordingly, it is desirable to provide plugs that are as short as possible while still having the requisite depth to provide sufficient mechanical (or “push out”) strength.
A challenge for simultaneously addressing all of these considerations involves plug depth variability. Plug depth variability is typically driven by differences in the flow rate of a plugging composition in different filter channels. Plugs in channels where there is relatively more resistance to flow tend to be shorter whereas plugs in channels where there is relatively less resistance to flow tend to be longer. Such variability can result in at least some relatively shorter plugs failing to provide requisite mechanical strength. Accordingly, given the ever increasing need to provide for shorter plugs, there simultaneously exists a need to provide for reduced plug depth variability in order to minimize the incidence of plugs that fail to provide requisite mechanical strength.